The IEEE (The Institute of Electrical and Electronics Engineers)1394 standard provides for physical and electrical standards of connectors provided on interconnection to respective equipments. The equipments having interfaces conforming to the IEEE 1394 standard can be physically interconnected to realize e.g., Hot Plug and Play adapted for automatically transmitting/receiving digital data speedily or establishing interconnection among different equipment. This is currently being accepted as a serial interface standard providing a criterium for the pertinent business circles.
It has recently been proposed in 1394 TRADE ASSOCIATION to receive printing data from an external network circuit by a set top box (STB) to print the data by a printer connected to the STB over the IEEE 1394 cable.
If, with the STB/DTV connected to the printer device, picture data acquired by the STB/DTV is to be printed using picture data acquired in the STB/DTV, the processing shown in FIG. 1 is carried out.
Referring to FIG. 1, the STB/DTV transmits a command packet C101, comprehending a command (SUBUNIT_INFO) inquiring into the information such as the type of the subunit (interfacing portion or picture processing portion) of the printing device, and receives a corresponding response packet R101. This permits the STB/DTV to recognize that the printing device is able to perform printing using the picture data.
Then, in order to verify whether or not printing with the image size and the image type at the time of printing can be made, the STB/DTV queries the printing device as to the form of printing.
At this time, the STB/DTV transmits to the printing device a capture command C102, inclusive of the information inquiring into whether or not the image size it is in need of is being coped with (SPECIFIC INQUIRY) to acquire the result of search comprehended in the response packet R102. The printing device 5 reads-in the corresponding portion (info block) of the subunit identity descriptor stated in itself to store the read-in portion as being the result of check in the response packet R102.
The STB/DTV then transmits to the printing device a capture command C103, comprehending the information inquiring into whether or not the image type it is in need of is coped with (SPECIFIC INQUIRY) to acquire the result of check included in the response packet R103.
This permits the STB/DTV to recognize whether or not the image size and the image sort it is in need of are coped with in the printing device.
However, if, in the above-described STB/DTV and the printing device, performing the processing described with reference to FIG. 1, the processing of querying the printing device as to two items of requests, namely the image size and the image sort, is to be performed, it is necessary that a packet for inquiring into whether or not the image sort is coped with be transmitted/received, and that a packet for inquiring into whether or not the image sort is coped with be then transmitted/received. That is, command and response packets need to be exchanged twice (C102 to R103).
Thus, a complicated processing sequence and prolonged processing time are needed for the STB/DTV to check into the printing device.
Moreover, dedicated descriptor accessing means need to be loaded for reading-in the subunit identity descriptor. In addition, the subunit identity descriptor is occasionally of a variable length, such that the processing of making analysis by descriptor accessing means sometimes becomes complex. On the other hand, the descriptor accessing means permits variable read-in methods, such as quadlet read, block read or offset utilization, and hence it is necessary to support respective read-in methods.
The present Applicant proposed the contents of the Japanese Patent Application No.H11-350865, which is the base of priority of the present application, to the IEEE 1394 Trade Association for standardization at suitable timing, and the contents of the proposal are made public as the following drafts by the IEEE 1394 Trade Association:
AV/C Printer Subunit Specification Version 1.0, Draft 0.97: 60 (2Q00 AVWG Off-Cycle Meeting on May 24-25, 2000);
AV/C Printer Subunit Specification Version 1.0, Draft 0.7: 5 (1Q00 TA QM AV-WG on Jan. 18, 2000); and
AV/C Printer Subunit Specification Version 1.0, Draft 0.5: 145 (3Q99 TA QM AVWG Meeting on Jul. 28-30, 1999).